I was processing well over $100,000/year in incoming transactions through my PayPal account when I was under 18. Any time my account was flagged for some reason or my debit card temporarily frozen (due to large transactions, that were made EVERY month on the same day to the same vendor... smart, right?), it was very easy to unlock the account again. Not sure how it is now, but I was able to get the business account phone reps to resolve my issues extremely quickly, and I never had to send in (and forge the age on) any verification of my information.
The real way to do it is to get your own merchant account, though. Your account won't be frozen due to chargebacks, and you'll actually be able to dispute the chargeback directly with the credit card companies or your merchant bank, and not have to go through an intermediary. You'll also be able to put in some good fraud fighting measures (depending on what product you use, if any) that can save a lot of aggrevation.
Google checkout is a pretty good system, but it's not as good as having a real merchant account. It's always a good backup, though.